The international meetings on mammary cancer are held alternatingly in the United States and Europe/Japan. At the last meeting (1978) in Detroit it was decided to have the 12th meeting in the Netherlands. The meeting provided a multidisciplinary discussion about the various factors involved in the genesis of mammary cancer in experimental animals as a model for the human disease. In the proposed program of the 12th meeting more emphasis is placed on the role of environmental factors, although the role of viruses will not be neglected. More attention than in the past will be placed on animal models for treatment and tumor-associated markers. The organizing committee has invited international scientists as chair persons for the seven separate sessions and twenty-five leading investigators as speakers. Their travel expenses will be covered by Dutch funds. The many other expected contributions will be presented in the form of posters. In view of the American dominance in mammary cancer research, it is anticipated that many U.S. investigators want to participate. Funds will be raised in the Netherlands to provide travel support for several scientists, but additional U.S. funds are necessary for this.